1. Field of the Invention
The present invention relates to: an image processing method which enables a zoom process of enlargement or reduction for image data as well as a dither process for producing halftone; an image processing apparatus for executing the method; an image forming system provided with the apparatus; and a recording medium which records a computer program for causing a computer to execute the method.
2. Description of Related Art
Conventionally, an image forming system for carrying out digital processing to a color image and outputting the image, such as an electrophotographic digital color multi function peripheral, an inkjet color printer or a thermal transfer color printer, is increasingly popular in the field of OA (Office Automation) equipments in which the digital technology is proceeding at a rapid rate.
For example, an image information, which is inputted from an input device such as a digital camera or an image scanner or created by a computer, is outputted from the above image forming system after a pseudo tone reproduction process (halftone process) is carried out for inputted image information.
An approach of the pseudo tone reproduction technology is a multi-level dithering process, in which a quantization process is performed for each pixel of a dither matrix shown in FIG. 15 (here, a number in each cell indicates the order of allocation of a dense output value), for example, on the basis of the magnitude relation with a plurality of thresholds corresponding respectively, to output any one of a plurality of output values or an output value converted on the basis of a conversion table.
Moreover, a conventional image forming system receives an output size of an image which is specified by the user and performs a zoom process depending on the received output size. For example, an output size of an image is enlarged by interpolating adjacent pixels or the like when a instruction for enlargement of an output size is received, or an output size of an image is reduced by downsampling pixels or the like when a instruction for reduction of an output size is received.
Regarding a conventional image forming system described above, various methods of image processing have been tested to smoothly execute a tone reproduction process and a zoom process. For example, Japanese Patent Application Laid-Open No. H1-136465 and Japanese Patent Application Laid-Open No. S60-97774 suggest methods for carrying out a tone reproduction process and a zoom process for image data.